alsocal*o*ryn, pl-ries 1 a : the amount of heat required at a pressure of one atmosphere to raise the temperature of one gram of water one degree Celsius that is equal to about 4.19 joules - abbr. cal - called also gram calorie , small calorie b : the amount of heat required to raise the temperature of one kilogram of water one degree Celsius that is equal to 1000 gram calories or 3.968 Btu - abbr. Cal - called also kilocalorie , kilogram calorie , large calorie 2 a : a unit equivalent to the large calorie expressing heat-producing or energy-producing value in food when oxidized in the body b : an amount of food having an energy-producing value of one large calorie .